This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. SPECIFIC AIMS: Primary Objectives: To determine the efficacy and safety of rituximab plus modified CODOX-M/IVAC regimen in patients with HIV-associated Burkitt s (BL) or atypical Burkitt s. The primary study endpoint is overall survival (OS) at one year, and secondary endpoints include complete response (CR) rate, failure-free survival (FFS), event-free survival, and toxicity. Secondary objectives: " Evaluate downstream effectors of apoptosis as mechanisms of chemotherapy resistance and prognosis and perform exploratory analysis of their relationship to treatment effect. " Evaluate multi-drug resistance gene expression as a mechanism of chemotherapy resistance and prognosis and perform exploratory analysis of their relationship to treatment effect. " Confirm the use of flow cytometry in the identification of occult leptomeningeal disease and determine whether abnormal flow cytometry is predictive of CNS cytology is negative for malignant cells. " Determine the biologic and prognostic significance of Epstein-Barr Virus (EBV) + Burkitt s Lymphoma (BL) in the highly active antiretroviral therapy (HAART) era and perform exploratory analysis of their relationship to treatment effect. " Evaluate genotyping in BL and determine whether it is similar to that described in HIV negative cases. Moreover, determine whether cases are uniform in their genetic profile or whether some cases are more like DLBCL. " Determine if EBV detection in CSF at diagnosis is predictive of leptomeningeal disease.